The present invention relates generally to restraint systems and more particularly to a method for controlling airbag deployment in automobiles.
It is well known to provide occupant restraint assemblies for vehicles, such as passenger cars, to restrain the occupant during a crash. Typically, an occupant restraint assembly includes a seat belt, an airbag and an inflator for inflating the airbag. When a crash occurs, as sensed by a crash sensor, the airbag is deployed by inflating it with gas.
In order to control the firing of an airbag in a collision, it is important to know the mass of the seat occupant. Weight sensors, such as bladders and pressure pads disposed in or under the seat, are available for measuring the vertical force of the occupant on the seat cushion. However, the seat belt can add an unknown quantity to this vertical force. For an adult occupant, this force is likely to be small, since a tightly cinched seat belt would be uncomfortable. However, for a child in a car seat this force can be large, since the seat belt is cinched around the seat, not the child, and the belt should be deliberately drawn tight to secure the car seat.
Devices are available that measure tension in the seat belt webbing. However, these devices suffer from several drawbacks. Reliable, unobtrusive electrical connections must be made to them through the belt webbing. In measuring tension, these devices do not sense the desired parameter, which is the vertical component of tension. The seat belt may wrap around the occupant through a range of angles, depending upon seat fore-aft location, size of occupant and whether the occupant is in a car seat. As such, a reliable estimate of the vertical component of force may not be attainable by these devices. In addition, the seat belt may have frictional or clamp forces on it if it feeds through child seat attachment slots, so that the tension of the belt changes with location.
It is thus highly desirable to provide a simple, reliable means of determining the vertical component of total force applied by the seat belt, so that it may be subtracted from the total vertical force measured by a seat cushion weight sensor.
It is thus an object of the present invention to provide a simple, reliable method for determining the vertical component of total force applied by the seat belt, which is then used to properly control the firing of an airbag during a collision.
This object is accomplished by providing force sensors at two, or if necessary, all three of the attachment pieces of the standard three-point lap belt. These sensors (strain gauges) measure the resistance at these attachment points. By sizing the nominal resistance of the two floor attachment bolt strain gauges, the two resistors can be put in a series circuit such that only the sum of the two resistances need be measured. The measurements obtained are then used to obtain the vertical components of force due to the seat belt. This value may then be subtracted from the total vertical force measured by a weight sensor in the seat cushion to determine the mass of the vehicle seat occupant.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.